Cancer is a major public health problem in worldwide. It is currently the second leading cause of death in the United States and in several developed countries, and is expected to surpass heart diseases as the leading cause of death in the next few years. (Siegel R L, et al, Cancer Statistics, 2015, CA Cancer J Clin 2015; 65:5-29. VC 2015 American Cancer Society and references therein).
Cancer is considers a complex disease that is dictated by both cancer cell-intrinsic and cell-extrinsic processes. Several studies conducted in various in vitro and animal models including, for example, lung metastasis, human lung adenocarcinoma cells, murine melanoma cells, murine ovarian cancer cells, murine breast cancer cells, have confirmed that targeting the adenosinergic system has tremendous potential to develop different treatments. A number of lines of evidence highlight the importance of adenosine as a critical regulatory autocrine and paracrine factor that accumulates in the neoplastic microenvironment. Extracellular adenosine, which is usually present at high concentrations in cancer tissues, is a crucial mediator in the alteration of immune cell functions in cancer. This is possibly because the tightly regulated adenosine receptor pathways of immune cells undergo substantial alterations in tumours, thereby switching the functions of these cells from immune surveillance and host defense to the promotion of cancer cell transformation and growth. (Antonioli L et al, Immunity, inflammation and cancer: a leading role for adenosine, Nature, 842, December 2013, Volume 13, and references therein).
As it is known tumors use numerous immunosuppressive mechanisms to facilitate tumor growth (Koebel C M. et al, Adaptive immunity maintains occult cancer in an equilibrium state, Nature. 2007, 450, 7171:903-907 and Schreiber R D. et al, Cancer immunoediting: Integrating immunity's roles in cancer suppression and promotion, Science. 2011, 331, 6024:1565-1570). There are studies establishing that one such mechanism was mediated by the catabolism of extracellular AMP into immunosuppressive adenosine (Ohta A. et al, A2A adenosine receptor protects tumors from antitumor T cells. Proc Natl Acad Sci USA. 2006; 103: 13132-13137 and Ohta A. et al, A2A adenosine receptor may allow expansion of T cells lacking effector functions in extracellular adenosine-rich microenvironments. J Immunol. 2009, 183, 9:5487-5493). Firstly, extracellular ATP will be converted to AMP by the ectoenzyme CD39. Further dephosphorylation of the AMP through the CD73 ectoenzyme will result in extracellular adenosine production.
During this process, activity of adenosine kinase is also suppressed causing the inhibition of salvage activity of this enzyme and an increase in adenosine levels. For example, under hypoxic conditions during inflammation or within tumor microenvironment, inhibition of adenosine kinase causes 15-20-fold increase in both extracellular as well as intracellular levels of adenosine (Decking U K. Et al, Hypoxia-induced inhibition of adenosine kinase potentiates cardiac adenosine release. Circ. Res. 1997; 81(2):154-164. doi: 10.1161/01.RES.81.2.154). The generated extracellular adenosine binds to four known cell surface receptors (A1, A2A, A2B, and A3) that are expressed on multiple immune subsets including T cells, natural killer (NK) cells, natural killer T cells, macrophages, dendritic cells, and myeloid-derived suppressor cells (MDSCs). The A2A and A2B receptor subtypes are essentially responsible for the immunosuppressive effects of adenosine. They share a common signalling pathway, both resulting in the activation of adenylate cyclase and the accumulation of intracellular cAMP. Several evidences have been further provided demonstrating that the intracellular cAMP is the signalling molecule that inhibits T-cell receptor signalling at early and late stages of T-cell receptor-triggered T-cell activating pathway. (Ohta A, Sitkovsky M, Role of G-protein-coupled adenosine receptors in downregulation of inflammation and protection from tissue damage, Nature, 2001, 414: 916-920).
It has been suggested that the elimination of A2a receptor genetically or the inhibition of A2a receptor signalling using A2a receptor antagonists prevents inhibition of anti-tumour T cells and improves tumour rejection (Ohta A. et al, A2a adenosine receptor protects tumors from antitumor T cells. Proc Natl Acad Sci USA. 2006; 103: 13132-13137).
A2a receptor functions as a non-redundant negative regulator of activated T cells to protect normal tissues from excessive collateral inflammatory damage. It has been proposed that A2a receptor may also ‘misguidedly’ protect cancerous tissues. It was reasoned that if this were indeed the case, then the genetic inactivation or pharmacological antagonism of A2a receptor would prevent the inhibition of anti-tumour T cells and thereby improve tumour rejection by these de-inhibited T cells (Sitkovsky M. et al, Adenosine A2a receptor antagonists: blockade of adenosinergic effects and T regulatory cells, British Journal of Pharmacology, 2008, 153, S457-S464).
Lung cancer is the leading cause of cancer death around the world and it has been the most common cancer worldwide since 1985, both in terms of incidence and mortality. Globally, lung cancer is the largest contributor to new cancer diagnoses (12.4% of total new cancer cases) and to death from cancer (17.6% of total cancer deaths).
Lung cancer arises from the cells of the respiratory epithelium and can be divided into two broad categories. Small cell lung cancer (SCLC) is a highly malignant tumor derived from cells exhibiting neuroendocrine characteristics and accounts for 15% of lung cancer cases. Non-small cell lung cancer (NSCLC), which accounts for the remaining 85% of cases, is further divided into 3 major pathologic subtypes: adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. Adenocarcinoma by itself accounts for 38.5% of all lung cancer cases, with squamous cell carcinoma accounting for 20% and large cell carcinoma accounting for 2.9%. In the past several decades, the incidence of adenocarcinoma has increased greatly, and adenocarcinoma has replaced squamous cell carcinoma as the most prevalent type of NSCLC. (De la Cruz, C et al, Lung Cancer: Epidemiology, Etiology, and Prevention, Clin Chest Med. 2011 December; 32(4)).
Particularly, in the case of NSCLC, disease stage determines the treatment, which includes surgery, radiation, platinum-based doublet chemotherapy and recently targeted therapies by interrupting signaling pathways responsible for cell proliferation and survival. Earlier stages of the disease benefit from systemic chemotherapy (platinum-doublet, taxanes, gemcitabine, pemetrexed) (Azzoli C G. et al, 2011 Focused Update of 2009 American Society of Clinical Oncology Clinical Practice Guideline Update on Chemotherapy for Stage IV Non-Small-Cell Lung Cancer, J Oncol Pract. 2012; 8:63-6 doi:10.1200/JOP.2011.000374), that results in modest efficacy, thus, multimodal therapeutic strategy has become an important treating option for NSCLC patients. In several studies, two or more drug combinations were proven to have superior efficacy but at the expense of added toxicity (Yoshida T. et al, Comparison of adverse events and efficacy between gefitinib and erlotinib in patients with non-small-cell lung cancer: a retrospective analysis, Med Oncol. 2013; 30:349).
Recently, several approaches are being developed to boost anticancer responses of T-cells and restore their ability to detect and attack cancer cells among them mAbs blocking the cytotoxic lymphocyte-associated antigen 4 (CTLA4) and the programmed cell death protein 1 (PD-1)-mediated T-cell events have been developed.
Ipilimumab, a fully human mAb against CTLA4, has shown a trend toward greater clinical benefit among patients with SQCLC (Lynch T J. et al, Ipilimumab in combination with paclitaxel and carboplatin as first-line treatment in stage IIIB/IV non-small-cell lung cancer: Results from a randomized, double-blind, multicenter phase II study, J Clin Oncol. 2012; 30: 2046-54). The PD-1 mAbs (MED14735, BMS-936558, BMS-936559) have demonstrated remarkable sustained tumour regressions in the heavily pre-treated advanced NSCLC patients (Brahmer J R. et al, Safety and activity of anti-PD-L1 antibody in patients with advanced cancer, N Engl J Med. 2012; 366: 2455-65).
There are studies showing the alterations provoking changes in the extracellular tumor microenvironment. One of such extracellular alterations is the increased adenosine concentrations, which impair T cell mediated rejection and support angiogenesis. The study showed a significant number of lung adenocarcinomas expressing adenosine A2a receptor, supporting tests of adenosine A2a receptor antagonists as anticancer therapies. (Mediavilla-Varela, M et al, Antagonism of adenosine A2a receptor expressed by lung adenocarcinoma tumor cells and cancer associated fibroblasts inhibits their growth, Cancer Biology & Therapy, September 2013, 14:9, 860-868).
Despite the development of new therapeutics, NSCLC still has a 5-year survival rate in only 14% implying the need for the continuing research for novel treatments (Spira A. et al, Multidisciplinary management of lung cancer, N Engl J Med. 2004; 350:379-92 doi: 10.1056/NEJMra035536).